Transferring quantum entangled states between multiple single-photon-state qubits and coherent-state qubits in circuit QED

TL;DR

This paper proposes a method for transferring entangled states between single-photon and coherent-state qubits in circuit QED using a single superconducting qutrit, enabling high-fidelity, deterministic transfer with minimal decoherence.

Contribution

It introduces a simplified circuit architecture for state transfer that does not increase in complexity with more qubits and suppresses decoherence by avoiding excitation of higher energy levels.

Findings

High-fidelity Bell state transfer demonstrated numerically

Operation time remains constant regardless of qubit number

Transfer process is deterministic and does not require measurement

Abstract

We present a way to transfer maximally- or partially-entangled states of n single-photon-state (SPS) qubits onto n coherent-state (CS) qubits, by employing 2n microwave cavities coupled to a superconducting flux qutrit. The two logic states of a SPS qubit here are represented by the vacuum state and the single-photon state of a cavity, while the two logic states of a CS qubit are encoded with two coherent states of a cavity. Because of using only one superconducting qutrit as the coupler, the circuit architecture is significantly simplified. The operation time for the state transfer does not increase with the increasing of the number of qubits. When the dissipation of the system is negligible, the quantum state can be transferred in a deterministic way since no measurement is required. Furthermore, the higher-energy intermediate level of the coupler qutrit is not excited during the entire operation and thus decoherence from the qutrit is greatly suppressed. As a specific example, we numerically demonstrate that the high-fidelity transfer of a Bell state of two SPS qubits onto two CS qubits is achievable within the present-day circuit QED technology. Finally, it is worthy to note that when the dissipation is negligible, entangled states of n CS qubits can be transferred back onto n SPS qubits by performing reverse operations. This proposal is quite general and can be extended to accomplish the same task, by employing a natural or artificial atom to couple 2n microwave or optical cavities.